It is known to influence and maintain the tension of catch selvage yarns in a loom in various ways. Without such efforts the tension changes as the yarn is withdrawn from the selvage yarn supply spool. The yarns are supplied by a so-called selvage spool rotatably mounted in the loom frame for producing the catch selvage of a fabric. The catch selvage is later cut off. The selvage yarn spool, hereafter referred to as supply spool, carries the selvage yarn wound onto the spool and the yarn diameter of the spool diminishes or becomes less and less as the yarn is used up during the weaving process. The yarn content or the diameter of the yarn wound onto the supply spool is sensed by a yarn follower roller. The tension on the yarn as it is pulled off the supply roller is influenced by a braking action, whereby the yarn follower roller and the brake components follow the variable diameter of the yarn coil wound onto the supply spool in response to a spring action. The follower roller and the brake components operate in synchronism.
It is known to influence and maintain a desired tension force on the catch selvage yarn or yarns with the aid of at least one so-called looping brake as shown in present FIG. 1 to be described in more detail below. These catch selvage yarns are pulled off the supply spool during weaving by the tension applied to the selvage yarn. The looping brake controls the rotation of the supply spool and thus the tension force on the yarn. These conventional looping brakes comprise a spring tensioned brake tape or belt that loops around a supply spool flange, whereby so-called tension peaks in the selvage yarns and respective yarn breaks are unavoidable. A desired constant tension cannot be applied to the selvage yarns and yarn breaks cannot be reduced with the help of a looping brake so that there is room for improvement in such a conventional looping brake system.
German Patent Publication DE 2,421,748 C2 (Kovar et al.) discloses an apparatus for equalizing the tension on two binding threads in a leno selvage device also employing a looping brake.
German Patent Publication DE OS 2,129,817 (Mullekom) discloses a thread brake for maintaining a constant thread tension in the leno threads of a leno device for forming a leno selvage in a fabric. The Mullekom thread brake includes a bail that reaches around the flange of the leno thread spool. The bail is mounted at the end of a mounting arm the other end of which is pivotably mounted between two support lugs on the leno disk. A sensor or follower roller is provided on one side of the bail and a tension spring connected to the mounting arm of the bail is effective to keep the follower roller in contact with the thread supply on the leno thread supply spool. Brake elements are provided on the bail for keeping the leno thread tension constant. These brake elements are effective on both sides of a flange of the leno thread supply spool. Such a structure has the disadvantage that the braking elements are effective directly on the flange of the leno thread supply spool which damages the spool body in a relatively short time to such an extent that the spool body must be replaced. The damage manifests itself in so-called brake track grooves which, when the spool body is reused or refilled with leno yarn, the yarn becomes entangled in the brake grooves when thread is being pulled off the supply spool, particularly on the yarn facing side of the spool flange, whereby the thread can get caught and stuck to eventually tear.